Method for bleeding a hydraulic system



Dec. 26, 1967 S. LAPOINTE METHOD FOR BLEEDING A HYDRAULIC SYSTEM 2Sheets-Sheet l Filed Sept.

/)v VENTOI? 51m ZAPO/NTE B Y PATENT AGENT Dec. 26, 1967 5, om 3,359,994

METHOD FOR BLEEDING A HYDRAULIC SYSTEM Filed Sept. 20, 1965 2SYIQWLS-Sl'K-lGt 2 wvgA/rok Simd'bn LAPO/NTE PATfNT AGENT United StatesPatent 3,359,994 METHOD FOR BLEEDING A HYDRAULIC SYSTEM Simon Lapointe,11764 James Morrice St., Montreal, Quebec, Canada Filed Sept. 20, 1965,Ser. No. 488,680 6 Claims. (Cl. 137-15) ABSTRACT OF THE DISCLOSURE Thisinvention relates to a method for bleeding a hydraulic motor connectedin a hydraulic system including a reservoir, a feeding circuit and areturn circuit between said motor and said reservoir, said motor havinga normally closed bleeding orifice, said method comprising the steps oftemporarily connecting an auxiliary hydraulic line to said bleedingorifice and to said return circuit and circulating hydraulic fluidthrough said motor, auxiliary line and return circuit back into saidreservoir until substantially all gas entrapped in said motor isreturned to said reservoir, wherein it becomes separated from the fluidand thereafter disconnecting said auxiliary hydraulic line and closingsaid bleeding orifice.

The present invention relates to a method and apparatus for bleedinghydraulic systems and, more specifically, the brake systems of aircraft.

In the conventional manner of bleeding aircraft wheel brakes, the fluidremoved from the hydraulic system is thrown away. This constitutes animportant waste because fluid, used in present-day aircraft hydraulicsystems, is very expensive. Moreover, this hydraulic fluid attacks paintand rubber, and any fluid spillage may be detrimental to the aircrafttires and to the paint on the aircraft.

The general object of the present invention residestherefore in a methodand means whereby practically all of the fluid bled from a hydraulicsystem, and more particularly from the hydraulic brake system of anaircraft, is returned directly to the reservoir of the same hydraulicsystem, or of a test rig, without spilling of the fluid and withoutcontaminating the same. The method and means in accordance with theinvention provide also a visual means of checking the quality of thebleeding function and result in much faster and positive bleedingoperation than the conventional method.

Another important object of the present invention resides in theprovision of an aircraft hydraulic system plumbing modified byinstalling a fluid returning fitting, equipped with a check valve, in aconveniently located line which performs a return function while thebleeding operation takes place, thereby to provide for quick and easybleeding of the brake system and for automatically returning the bledfluid back into the general hydraulic system of the aircraft.

Another important object of the present invention re- 7 sides in theprovision of a method and means for bleeding a hydraulic system of thecharacter described, which may be used for bleeding any part of thehydraulic system of an aircraft, or of hydraulic systems of othermachines.

The method and means in accordance with the invention consistessentiallyin connecting either a temporary or permanent auxiliaryhydraulic line between the bleeder port of a hydraulic component to bebled, and a connection in a hydraulic line in the return circuit of thehydraulic system, or directly to the reservoir of the aircraft system ortest rig reservoir, and to circulate fluid through said circuit thusestablished, until practically all of the gas entrapped in the fluid, iscarried back into the hydraulic reservoir, where the gas becomesseparated from the fluid.

3,359,994 Patented Dec. 26, 1967 The foregoing and other importantobjects of the present invention will become more apparent during thefollowing disclosure and by refer-ring to the drawings, in which:

FIGURE 1 is a partial perspective view of the aircraft landing gear of atype such as found on DC-S. jet aircraft;

FIGURE 2 is a top plan view of the bleed harness used in accordance withthe invention;

FIGURE 3 is a partial elevation, and partially in section, of thehydraulic circuit of the UNLOCK line, connected to the bogie swivelunlock cylinder, at the front lower end of the main landing gear shockstrut cylinder, in accordance with FIGURE 1, said line being modified inaccordance with the invention;

FIGURE 4 is a cross-section and schematic view of a hydraulic brakeactuating cylinder, of one wheel of the landing gear and also showingthe supply line and lockout cylinder associated therewith; and FIGURE 5is a schematic view of a hydraulic system showing the locations of thetemporary or permanent auxiliary line connections used for bleeding.

Referring now more particularly to the drawings in which like referencecharacters indicate like elements throughout, FIGURE 1 shows, insomewhat schematic manner, one side of the main landing gear of a DC-8aircraft comprising a shock strut 1, at the lower end of which ismounted a bogie assembly 2, made of a forward bogie 4 and aft bogie 3,the bogie assembly carrying a pair of rear wheels 5 and a pair of frontwheels 6. Each wheel is equipped with a hydraulic brake assembly.

The wheel brake carrier 7 of each wheel is provided with the usualbleeding port closed by a bleeder valve screw 8. The bleeding orifice isshown at 9, in FIGURE 4, and is in communication with the inside of thebrake actuating cylinder, partially shown at 10. The bleeding orifice 9forms a tapered seat 11 for receiving the pointed tip of the bleedervalve screw 8 and said bleeder valve screw 8 is provided with aninverted T-shaped bore 12, the cross leg of which opens at the taperedend of the bleeder valve screw to be closed by seat 11 when bleedervalve screw 8 is screwed tight within bleeding orifice 9. The main legof bore 12 extends to the outer end of the bleeder valve screw and isinternally threaded and closed by screw plug 13. a

For conventional bleeding of the brake actuating cylinder 10, screw plug13 is first removed, a hose is connected to bore 12 and then bleedervalve screw 8 is slightly unscrewed to allow the fluid and air,entrapped in the fluid, to be discharged through the T bore 12.

FIGURE 4 shows also, in schematic manner, the usual lock-out cylinder 14connected in the supply line 15 of the hydraulic brake actuatingcylinder 10. Lock-out cylinder 14 has a piston 16 provided with a pistonrod 17 having an axial bore 17 closed by bleeder valve screw 8 and screwplug 13. The supply line 15 is provided with a cylinder by-pass conduit18 having a normally closed valve 19. A lock-out cylinder 14 is providedfor each pair of wheel brakes, to prevent loss of fluid in the event offailure of one brake line, thus limiting the hydraulic fluid loss tothat contained downstream of the brake lock-out cylinder.

Referring to FIGURE 1, the usual bogie swivel unlock cylinder 20' ismounted on forward bogie 4 and serves, when pressurized in the unlockeddirection, to allow trailing action of the rear wheels 5 of the bogielocated on the hydraulic reservoir through the return side of thehydraulic system of the aircraft.

In accordance with the invention, as shown in FIGURE 3, the UNLOCK line21 of the bogie swivel unlock cylinder is fitted with a T-shaped conduit22 series-connected in the UNLOCK line 21, and having a lateral branch23 provided with a check valve 24 allowing entrance of bleeding fluidwithin the conduit 22, but preventing discharge of fluid therefrom.

The unconnected end of check valve 24 is normally closed by a screw cap25. The T 22 is connected just above the manifold 26, in turn having aline connected at 27 to the UNLOCK side of the bogie swivel unlockcylinder 20. Thus, the T-shaped conduit 22 will be located along theshock strut 1, closed to the four bleeder valve screws 8 of the fourwheel brakes.

A harness, shown in FIGURE 2, is used to constitute an auxiliaryhydraulic line and is temporarily connected between the four bleedervalve screws 8 and the check valve 24 in the bogie swivel UNLOOKcircuit, said circuit being normally connected to the fluid reservoir ofthe main hydraulic system of the aircraft.

The harness, shown in FIGURE 2, comprises an H- shaped rigid conduit 29,to the four branches of which are connected flexible hoses 30. The crossleg of the H-shaped conduit 29 is formed by a T coupling 31, to thelateral branch of which is connected a sight glass assembly 32comprising a transparent tube 33 and to the other end of which isconnected a flexible hose 34, in turn having at its outer end aconnection 35, to be adapted and to be removably connected to the checkvalve 24 after screw cap has been removed.

The outer ends of each of the four flexible hoses are fitted withstraight or L-shaped adaptors 36 terminated by an externally threadednipple 37, of reduced diameter, adapted to be screwed into the bore 12of bleeder valve screw 8, to replace the screw plug 13 of the bleedervalve screws 8 of each wheel brake. The T-shaped conduit 22 with itscheck valve 24 and screw cap 25 are permanently installed in the UNLOCKline 21 of the bogie swivel unlock cylinder 20, as previously described.

The bleeding procedure for all four brakes is as follows:

The brake lock-out cylinder by-pass valves 19 are opened and parkingbrakes are set to on. The screw plug 13 of all four brakes are removedand adaptors 36 are screwed in place thereof, said adaptors having beenpreviously disconnected from flexible hoses 30 of harness shown inFIGURE 2. Then, the hoses 30 are re-connected to the adaptors 36 and theconnection of the return hose 34 of the harness is connected to thecheck valve 24 after removal of screw cap 25. Thus, the harness, shownin FIGURE 2, constitutes an auxiliary line between the bleeding ports ofthe four brakes and the return circuit of the aircraft hydraulic system,said return circuit being the UNLOCK line of the bogie swivel unlockcylinder, which is normally internally connected to the fluid reservoir.

The brake bleeder valve screws 8 are opened one at a time and left openwhile hydraulic fluid is caused to be circulated by the pump of thehydraulic system through the associated hydraulic brake actuatingcylinder being bled. The fluid is thus circulated until all the air inthe fluid is returned to the reservoir of the hydraulic system. This isshown when air free fluid flows through the sight glass 33.

After pressurizing the hydraulic system, the bleeder valve screw 8 isscrewed back; the procedure is repeated for each brake in succession;the harness, shown in FIG- URE 2, is then removed and the screw plugs 13are screwed back in position in bleeder valve screws 8. The blanking cap25 is screwed back into position on the check valve 24; then, blankingcaps are screwed on connection 35 and adaptor nipples 37 of the bleedingharness.

The aircraft pump has been found to be powerful enough to circulate thehydraulic fluid at suflicient velocity to carry back into the fluidreservoir all of the air or other gas entrapped in the fluid.

The lock-out cylinders 14 may be bled in the same manner by usingharness 28; the adaptors 36 are connected to the bleeder valve screws 8of piston rods 17 of the look-out cylinders and harness connection 35connected to the bogie unlock line bleed connection at check valve 24.Fluid is successively circulated through the lockout cylinders 14 withtheir associated by-pass valves 19 opened, until air-free fluid appearsthrough the sight glass. Then, the harness is disconnected, the screwplugs 13 are put back in position together with screw cap 25, and thelock-out cylinder by-pass valves 19 are closed.

If less than four wheel brakes are being bled, the unused hoses 30 aredisconnected from the H-shaped coupling 29 and the open branches of thelatter are capped. Any other sub-system or component, such as the wingflap cylinders of the hydraulic system of an aircraft, or of any othermachine, may be bled in the above-noted manner. As shown schematicallyin FIGURE 5, the method is applicable to a hydraulic system comprising ahydraulic motor such as hydraulic cylinder 38, a feeding circuit 39permanently or temporarily mounted and including a hydraulic pump 40, orother device for circulating the fluid under pressure, a control valve41, a reservoir 44 which may be pressurized, and a return circuit 43,permanently or temporarily mounted, the return circuit 43 beingconnected to valve 41 and the reservoir, while the feeding circuit 3% isconnected to the reservoir and valve 41.

The hydraulic actuating cylinder 38 has a normally closed bleedingorifice 45 and the method in accordance with the invention consists intemporarily connecting an auxiliary hydraulic line 46 to the returncircuit 43 and to the bleeding opening 45 and circulating fluid throughthe feeding circuit into the hydraulic actuating cylinder 38 and back tothe reservoir 44 through the auxiliary line 46 and return circuit 43 atsuch a rate and for a time sufiicient that substantially all of the airentrapped in the fluid is carried back into the reservoir 44, where itwill become separated from the fluid.

While a preferred embodiment in accordance with the invention has beenillustrated and described, it is understood that various modificationshave been illustrated and described without departing from the scope ofthe appended claims.

What I claim is:

1. A method for bleeding a hydraulic motor connected in a hydraulicsystem including a reservoir, a feeding circuit and a return circuitbetween said motor and said reservoir, said motor having a normallyclosed bleeding orifice, said method comprising the steps of temporarilyconnecting an auxiliary hydraulic line to said bleeding orifice and tosaid return circuit, circulating fluid through said motor, auxiliaryline and return circuit into said reservoir until substantially all gasentrapped in said motor is returned to said reservoir wherein it becomesseparated from said fluid, and thereafter disconnecting said auxiliaryhydraulic line, and closing said bleeding orifice.

2. A method for bleeding a hydraulic motor connected in a hydraulicsystem including a reservoir, a feeding circuit and a return circuitbetween said motor and said reservoir, said motor having a normallyclosed bleeding orifice, comprising the steps of temporarily connectingan auxiliary hydraulic line to said bleeding orifice and to said returncircuit and circulating hydraulic fluid through said feeding circuit,said motor, said auxiliary line and said return circuit back into saidreservoir at a sufiicient speed to carry substantially all gas entrappedin said motor and circuits back into said reservoir, wherein said gasbecomes separated from said fluid, and thereafter disconnecting saidauxiliary line, and closing said bleeding orifice.

3. A method for bleeding a hydraulic motor connected in a hydraulicsystem including a reservoir, a feeding Circuit and a return circuitbetween said motor and said reservoir, said motor having a bleedingorifice, comprising the steps of temporarily connecting an auxiliaryhydraulic line having a series-connected sight glass, to said bleedingorifice and to said return circuit, circulating hydraulic fluid throughsaid feeding circuit, motor, said auxiliary line and said return circuitback into said reservoir at a sufficient speed to carry gas entrapped insaid motor and circuits back into said reservoir and until fluid seen insaid sight glass is substantially gas-free and thereafter disconnectingsaid auxiliary line, and closing said bleeding orifice.

4, A method for bleeding a hydraulic motor connected in a hydraulicsystem including a valve, a hydraulic line connected to said motor andto said valve, means feeding hydraulic fluid under pressure, a pressureline connected to said valve and to said means, a reservoir connected tosaid means, and a return line connected to said valve and to saidreservoir, said motor having a normally closed bleeding orifice, saidmethod comprising the steps of temporarily connecting an auxiliaryhydraulic line to said bleeding orifice and to said return line andoperating said means to supply fluid under pressure to said motor untilsubstantially all gas entrapped n the motor is carried by said fluidback into said reservoir, wherein said gas becomes separated from saidfluid, and thereafter disconecting said auxiliary hydraulic line, andclosing said bleeding orifice.

5. A method for bleeding the hydraulic cylinders of the wheel brakes ofan aircraft landing gear, said cylinders having a normally closedbleeding orifice and connected in a hydraulic system including a feedingcircuit connected to said cylinders, a reservoir connected to saidfeeding circuit, a return circuit connected to said reservoir and afluid line at least temporarily connected to said return circuit, saidmethod comprising the steps of temporarily connecting an auxiliaryhydraulic line to said bleeding orifices and to said fluid line andcirculating fluid through said feeding circuit, said motor, saidauxiliary line, said fluid line and said return circuit back into saidreservoir until substantially all gas entrapped in the cylinders iscarried back into said reservoir wherein said gas becomes separated fromsaid fluid, and thereafter disconnecting said auxiliary line and closingsaid bleeding orifices.

6. A method as claimed in claim 5, wherein said aircraft landing gearcomprises a bogie and a bogie swivel unlock cylinder, a hydraulic unlockline for said unlock cylinder, said fluid line consisting of saidlast-named hydraulic unlock line.

References Cited UNITED STATES PATENTS 2,295,539 9/1942 Beach 188l522,644,548 7/ 1953 Schiemann 188152 2,653,564 9/1953 Benefield 116-1182,771,093 11/1956 Wilson 137614.17 2,930,552 3/1960 Hartel 244-1053,154,087 10/1964 Beaver 137-15 30 HENRY T. KLINKSIEK, Primary Examiner.

1. A METHOD FOR BLEEDING A HYDRAULIC MOTOR CONNECTED IN A HYDRAULICSYSTEM INCLUDING A RESERVOIR, A FEEDING CIRCUIT AND A RETURN CIRCUITBETWEEN SAID MOTOR AND SAID RESERVOIR, SAID MOTOR HAVING A NORMALLYCLOSED BLEEDING ORIFICE, SAID METHOD COMPRISING THE STEPS OF TEMPORARILYCONNECTING AN AUXILIARY HYDRAULIC LINE TO SAID BLEEDING ORIFICE AND TOSAID RETURN CIRCUIT, CIRCULATING FLUID THROUGH SAID MOTOR, AUXILIARYLINE AND RETURN CIRCUIT INTO SAID RESERVOIR UNTIL SUBSTANTIALLY ALL GASENTRAPPED IN SAID MOTOR IS RETURNED TO SAID RESERVOIR WHEREIN IT BECOMESSEPARATED FROM SAID FLUID, AND THEREAFTER DISCONNECTING SAID AUXILIARYHYDRAULIC LINE, AND CLOSING SAID BLEEDING ORIFICE.